welding undercut

Welding Undercut Definition + What Is Undercutting In Welding?

What is Undercut in Welding?

In welding, undercut refers to a groove that forms at the base of the weld joint where the weld metal has melted away from the base metal. Essentially, the weld pool erodes the base material along the edges of the weld bead, creating a channel or depression in the base metal. 

Undercutting can weaken the joint and reduce the overall strength of the welded structure. Therefore, it is crucial to understand the causes and effects of undercutting in welding and take appropriate measures to prevent or repair it.

Welding undercut definition

Undercut can also be defined as a local reduction in the thickness of the base metal that occurs along the weld joint due to improper welding techniques, equipment setup, or welding parameters.

Why is undercut bad in welding?

bad welding undercut

Undercutting in welding is a type of weld defect that can have negative effects on the strength and integrity of the weld joint. When a groove or notch is formed in the base metal adjacent to the weld, it causes a reduction in the cross-sectional area of the joint, which can lead to reduced strength, cracking, corrosion, and aesthetic issues. This is especially critical in applications where the welded structure is subjected to high loads. 

Understanding undercutting in welding is important because it can help welders identify the causes and take appropriate measures to prevent it. By using proper welding techniques, preparing the joint correctly, and maintaining the welding equipment, welders can reduce the risk of undercut and ensure a strong and durable weld joint.

Different types of welding undercut

There are several different types of welding undercuts. Understanding the different types of welding undercuts can help welders identify the specific causes and take appropriate measures to prevent or repair it. We have listed them below:

Linear undercut:

Linear undercut is a continuous groove that runs along the length of the weld. It can be caused by welding too quickly or using an incorrect electrode angle.

Arc strike undercut:

Arc strike undercut occurs when the arc is started or stopped in the same place repeatedly, causing a depression in the base metal. It can also be caused by using too high of an amperage when starting or stopping the arc.

Root undercut:

Root undercut is a groove that forms at the root of the weld joint, between the base metal and the first layer of weld metal. It can be caused by inadequate heat input, poor joint preparation, or incorrect welding technique.

Side wall undercut:

Side wall undercut occurs when the edges of the weld bead are not properly fused to the base metal, resulting in a groove along the side of the weld. It can be caused by using too high of an amperage or an incorrect electrode angle.

Contact tip undercut:

Contact tip undercut occurs when the contact tip of the welding gun touches the base metal during welding, causing a groove in the metal. It can be caused by using an incorrect contact tip size or improper technique.

Causes of welding undercut

Understanding the causes of welding undercut is crucial for welders to prevent this type of weld defect from occurring. By identifying the causes of welding undercut, welders can take appropriate measures to prevent it from occurring and ensure a strong and durable weld joint. In the following section, we will discuss the common causes of welding undercut and how to prevent it.

Excessive welding current or voltage:

If the welding current or voltage is too high, the weld pool may become too fluid, which can lead to excessive melting of the base metal and the formation of undercut.

Welding at high speed:

Welding too quickly can result in insufficient heat input, which can cause the weld pool to become narrow and deep, leading to undercut.

Improper electrode angle or arc length:

Using the wrong electrode angle or arc length can cause the electrode to melt the base metal excessively, leading to the formation of undercut.

Inadequate filler material:

If the filler material is not added properly, it can cause a lack of fusion between the base metal and the filler metal, which can lead to undercut.

Incorrect joint preparation:

If the joint is not properly prepared before welding, it can cause uneven melting of the base metal, leading to undercut.

Poor shielding gas coverage:

If the shielding gas is not adequate or properly distributed, it can cause oxidation of the base metal, which can lead to the formation of undercut.

Equipment issues:

Equipment malfunctions or inadequate maintenance can cause problems with the welding process, leading to the formation of undercut.

Prevention of welding undercut

Preventing welding undercut is crucial for welders to ensure a strong and durable weld joint. By taking appropriate measures to prevent welding undercut, welders can ensure that the weld joint meets the desired quality standards and avoid the costs associated with repairing or re-welding the joint. 

In the following section, we will discuss the best practices for preventing welding undercut, including proper preparation of the joint, choosing the right welding parameters, and maintaining the welding equipment.

Use the correct welding technique: Proper welding technique, including maintaining the correct electrode angle, arc length, and travel speed, can help prevent undercut.

Use the correct welding parameters: Using the correct welding parameters, such as voltage, amperage, and wire feed speed, can help prevent excessive melting of the base metal and the formation of undercut.

Properly prepare the joint: Proper joint preparation, including cleaning and bevelling the edges of the base metal, can help ensure proper fusion and prevent undercut.

Use the correct filler metal: Using the correct filler metal for the base metal and welding process can help prevent lack of fusion and the formation of undercut.

Ensure adequate shielding gas coverage: Proper shielding gas coverage can help prevent oxidation of the base metal, which can lead to undercut.

Properly maintain equipment: Regularly inspecting and maintaining welding equipment, including checking for worn or damaged parts, can help ensure proper welding and prevent undercut.

Practice on scrap material: Practicing on scrap material can help welders refine their technique and identify any issues that may lead to undercut.

How to fix welding undercut (Remedies)

If left unaddressed, welding undercut can lead to a range of issues such as cracking, corrosion, and aesthetic problems. 

Fortunately, there are several methods to fix welding undercut, depending on the severity of the defect and the welding process used. 

In this section, we will discuss some effective remedies for welding undercut, including grinding, filling, and welding over the defect. We will also provide tips on how to choose the best approach based on the specific welding situation, and how to ensure a strong and durable weld joint.

Different welding undercut repair methods

Grinding: Grinding is the most common method for fixing minor welding undercut defects. This process involves using an abrasive wheel or disc to remove the undercut and blend it with the surrounding metal. This method works well for small undercut defects that are less than 1/16 inch deep.

Filling: Filling involves using a welding rod or wire to fill the undercut defect with weld metal. This method is effective for deeper and wider undercut defects. The weld metal is then ground to blend with the surrounding metal, creating a smooth surface.

Welding over the defect: Welding over the defect involves applying additional weld metal over the undercut to fill it. This method works well for shallow undercut defects and is best done using the same welding process that was used to create the original weld joint.

When fixing a welding undercut, it is important to choose the best approach based on the specific welding situation. The welder should also ensure that the repaired area is free from any contaminants and that the welding equipment is properly calibrated. By taking the appropriate measures, welders can ensure a strong and durable weld joint and prevent any further damage to the structure.

When to repair welding undercut

Welding undercut should be repaired as soon as it is detected to prevent any further damage to the weld joint. Even minor undercutting can compromise the strength and integrity of the weld joint and can lead to cracking, corrosion, and other issues over time.

The severity of the undercut and the specific welding application will determine when welding undercut should be repaired. In some cases, minor undercutting can be tolerated, while in other cases, even small defects may require repair. Let us know in the comments if you have experienced this. 

Welding codes and standards often provide guidelines for the acceptable level of undercutting, and welders should follow these guidelines when evaluating and repairing undercut defects. In addition, welders should regularly inspect weld joints for signs of undercutting and repair any defects promptly to ensure the safety and reliability of the structure.

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